Network construction type converter system and method based on three voltage sensors and one current sensor

Abstract

The invention provides a network construction type converter system and method based on three voltage and one current sensor, and relates to the technical field of power electronics, and the network construction type converter system comprises a DC voltage sensor, a DC current sensor, and two AC capacitor voltage sensors. The DC voltage sensor is used for calculating the duty ratio in a voltage inner loop, the DC current sensor is used for reconstructing three-phase phase current on an inversion side, the three-phase phase current on the inversion side is used for power calculation and current limiting protection, and the AC capacitor voltage sensor is used for inner loop capacitor voltage control and sampling of two-phase capacitor voltage. And calculating the residual phase capacitor voltage by using the Kirchhoff voltage law, and performing grid-connected pre-synchronization control by using the alternating current capacitor voltage sensor.

Description

Technical Field

[0001] The present disclosure relates to the field of power electronics technology, and particularly to a network-forming converter system and method based on three voltage sensors and one current sensor. Background Art

[0002] The statements in this section merely provide background technical information related to the present disclosure and do not necessarily constitute prior art.

[0003] The network-forming converter has broad application prospects in the new power system. It has flexible frequency modulation / voltage regulation capabilities, can actively provide grid auxiliary service functions such as inertia and damping, and has strong adaptability under weak grids. In addition, the network-forming converter can achieve synchronization with the grid without relying on a phase-locked loop and can autonomously construct voltages, so seamless grid connection / disconnection can be realized. Under extreme conditions, the network-forming converter is also equipped with fault ride-through and black start functions.

[0004] The network-forming converter usually includes multiple high-precision voltage / current sensors. The mainstream network-forming converter system requires 13 voltage / current sensors to achieve complete control functions, including: 3 capacitor voltage sensors, 3 PCC voltage sensors, 3 inverter-side current sensors, 3 grid-side current sensors, and 1 DC-side voltage sensor. Among them, the capacitor voltage sensor is used for inner-loop capacitor voltage control, the inverter-side current sensor is used for current inner-loop control and over-current protection in the double closed-loop, the grid-side current sensor is used for power calculation, the PCC voltage sensor participates in grid connection pre-synchronization, and the DC-side voltage sensor participates in duty cycle calculation. The large number of high-precision sensors results in high cost and low reliability of the converter system, reducing its market competitiveness. Summary of the Invention

[0005] To solve the above problems, the present disclosure proposes a network-forming converter system and method based on three voltage sensors and one current sensor, designs a feed-forward type pre-synchronization control strategy, directly connects to the grid for synchronization through the capacitor voltage, removes the PCC voltage sensor, and adopts a phase current reconstruction strategy based on a DC current sensor to remove the AC current sensor on the basis of ensuring power calculation and fault current limiting protection of the network-forming converter. A network-forming converter system that only uses three voltage sensors and one current sensor is obtained, reducing the cost and volume of the network-forming converter.

[0006] According to some embodiments, the present disclosure adopts the following technical solutions: A network-forming converter system based on three voltage sensors and one current sensor, wherein the network-forming converter system includes a total of three voltage sensors and one current sensor; Among them, the voltage sensor includes a DC voltage sensor and two AC capacitor voltage sensors, and the current sensor is a DC current sensor. The DC voltage sensor is used to calculate the duty cycle in the inner voltage loop. The DC current sensor is used to reconstruct the three-phase phase currents on the inverter side. The three-phase phase currents on the inverter side are used for power calculation and current limiting protection. The AC capacitor voltage sensors are used for inner-loop capacitor voltage control, sampling the two-phase capacitor voltages, calculating the remaining phase capacitor voltage, and performing grid connection pre-synchronization control using the AC capacitor voltage sensors.

[0007] Further, the grid-forming converter system with three voltage and one current sensors specifically includes a DC voltage sensor, a DC current sensor, and two AC capacitor voltage sensors. The two AC capacitor voltage sensors sample the two-phase capacitor voltages, and the remaining phase is calculated by Kirchhoff's voltage law. The voltage collected by the AC capacitor voltage sensors is the core controlled quantity. At the same time, the AC capacitor voltage sensors are also used in grid connection pre-synchronization control. Voltage pre-synchronization control is achieved by the time sequence coordination of voltage reference value feedforward control combined with the output of the inner loop. Phase pre-synchronization control is achieved by the phased coordination of the phase of the capacitor voltage locked by the phase-locked loop and the output phase of the active power control.

[0008] Further, voltage pre-synchronization control is achieved by adding a voltage reference value feedforward link in the inner voltage loop. The phase-locking and grid connection front are moved from the PCC to the filter capacitor. Adding voltage feedforward in the inner voltage loop ensures that the voltage on the inverter side is controlled to the grid voltage at the moment of grid connection. The output of the voltage loop control is output after a certain time interval or directly after grid connection startup. The output of the voltage loop control is regarded as the adjustment amount of the voltage on the inverter side.

[0009] Further, phase pre-synchronization control includes two stages. In stage 1, the AC relay is closed, and the phase of the capacitor voltage locked by the phase-locked loop is obtained. In stage 2, that is, when grid connection pre-synchronization is started, the output phase of the phase-locked loop remains unchanged. At the same time, the output phase of the active power control adjusts the phase of the system coordinate transformation and pre-synchronization, and the grid-forming converter is started.

[0010] According to some embodiments, the present disclosure adopts the following technical solutions: A grid-forming converter system and method based on three voltage and one current sensors, wherein the control method consists of three parts, namely a feedforward type grid connection pre-synchronization control part, an inner and outer loop control part, and a phase current reconstruction part.

[0011] Furthermore, the phase pre-synchronization control in the feed-forward grid-connected pre-synchronization control includes two stages. In the first stage, the AC relay is closed and the phase of the locked-phase capacitor voltage is locked. In the second stage, the output phase of the phase-locked loop remains unchanged, and the phase deviation is generated by the active power control. The two are accumulated to obtain the phase of the system coordinate transformation. The voltage pre-synchronization control is realized by adding a voltage reference feed-forward link to the voltage inner loop. The phase-locking and grid-connection front are moved from the PCC to the filter capacitor. Adding voltage feed-forward in the voltage inner loop ensures that the inverter-side voltage is controlled to the grid voltage at the moment of grid connection. The output of the voltage loop control can be output after a period of time after grid connection is started, or can be directly output, regarded as the adjustment amount of the inverter-side voltage.

[0012] According to some embodiments, the present disclosure adopts the following technical solutions: A computer program product includes a computer program, and when the computer program is executed by a processor, it implements the method of the grid-forming converter system based on three voltage and one current sensors.

[0013] According to some embodiments, the present disclosure adopts the following technical solutions: A non-transitory computer-readable storage medium is used to store computer instructions, and when the computer instructions are executed by a processor, it implements the method of the grid-forming converter system based on three voltage and one current sensors.

[0014] According to some embodiments, the present disclosure adopts the following technical solutions: An electronic device includes: a processor, a memory, and a computer program; wherein, the processor is connected to the memory, the computer program is stored in the memory, and when the electronic device runs, the processor executes the computer program stored in the memory so that the electronic device executes and implements the method of the grid-forming converter system based on three voltage and one current sensors.

[0015] Compared with the prior art, the beneficial effects of the present disclosure are: The grid-forming converter system of the present disclosure based on three voltage and one current sensors includes a DC voltage sensor, a DC current sensor, and two AC capacitor voltage sensors. Compared with the mainstream grid-forming converter topologies, the number of sensors is reduced by more than 60%. The DC voltage sensor is used for the duty cycle calculation link in the voltage inner loop. The DC current sensor reconstructs the three-phase phase current on the inverter side, and this inverter-side phase current will be used for power calculation and current limiting protection. The AC capacitor voltage sensors are used for the inner-loop capacitor voltage control, sampling the two-phase capacitor voltages, and the remaining phase capacitor voltage is obtained using Kirchhoff's voltage law. And the AC capacitor voltage sensors will also be used in the grid-connected pre-synchronization control. This feed-forward pre-synchronization control method has a simple control structure, does not require a PCC voltage sensor, and has a fast pre-synchronization speed.

[0016] The control method of the grid-forming converter system based on three voltage and one current sensors of the present disclosure has a simple implementation process and does not require additional hardware. On the basis of ensuring the grid connection pre-synchronization, power calculation and current limiting protection functions of the grid-forming converter, only four voltage / current sensors are used, reducing the system cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] The accompanying drawings forming a part of this disclosure are used to provide a further understanding of the present disclosure. The schematic embodiments and descriptions thereof of the present disclosure are used to explain the present disclosure and do not constitute an improper limitation to the present disclosure.

[0018] Figure 1 It is a schematic diagram of the sensor configuration of a traditional typical three-phase grid-forming converter; Figure 2 It is a schematic diagram of the sensor configuration of a three-phase grid-forming converter based on three voltage and one current sensors according to an embodiment of the present disclosure; Figure 3 It is a control structure for implementing the removal of the AC current sensor and the PCC voltage sensor according to an embodiment of the present disclosure; Figure 4 It is a schematic diagram of the phase pre-synchronization in the feed-forward type pre-synchronization control according to an embodiment of the present disclosure; Figure 5 It is a schematic diagram of the corresponding relationship between the DC current and the inverter-side phase current during different effective vector action periods and the distribution range of the reconstruction dead zone in the traditional phase current reconstruction technology; Figure 6 It is the simulation result of the grid connection pre-synchronization and power control of the grid-forming converter according to an embodiment of the present disclosure. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0019] The present disclosure will be further described below in conjunction with the accompanying drawings and embodiments.

[0020] It should be noted that the following detailed descriptions are all illustrative and are intended to provide further explanations of the present disclosure. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by those of ordinary skill in the technical field to which the present disclosure belongs.

[0021] It should be noted that the terms used herein are only for describing specific embodiments and are not intended to limit the exemplary embodiments according to the present disclosure. As used herein, unless the context clearly indicates otherwise, the singular forms are also intended to include the plural forms. In addition, it should be understood that when the terms "comprising" and / or "including" are used in this specification, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof.

[0022] Embodiment 1 In an embodiment of the present disclosure, a grid-forming converter system based on three voltages and one current sensor is provided, including a DC voltage sensor, a DC current sensor, and two AC capacitor voltage sensors. The DC voltage sensor is used to calculate the duty cycle in the voltage inner loop. The DC current sensor is used to reconstruct the three-phase phase currents on the inverter side. The three-phase phase currents on the inverter side are used for power calculation and overcurrent protection. The AC capacitor voltage sensors are used for inner-loop capacitor voltage control, sampling the two-phase capacitor voltages, calculating the remaining phase capacitor voltages using Kirchhoff's voltage law, and performing grid connection pre-synchronization control using the AC capacitor voltage sensors.

[0023] As Figure 1 shown, Figure 1 Fig. is the sensor configuration of a traditional typical three-phase grid-forming converter. There are a total of 13 voltage / current sensors in the topology of this grid-forming converter. Among them, the v gfabc collected by the capacitor voltage sensor is the core controlled quantity, and the i giabc collected by the current sensor on the inverter side is used for current inner-loop control and overcurrent protection in the double closed-loop. The i ggabc collected by the grid-side current sensor participates in power calculation. The v gabc collected by the PCC voltage sensor is used for grid connection pre-synchronization. The v gdc collected by the DC voltage sensor is used for the duty cycle calculation link in the voltage inner loop. In addition, S g1 - S g6 are power semiconductor switching devices. The inverter-side inductor L gi , the filter capacitor C gf and the grid-side inductor L gg form a three-phase LCL filter. The ideal voltage source v sabc and the equivalent inductor L s are connected in series to simulate the power grid. S g_relay is a three-phase AC relay.

[0024] The present disclosure improves the control structure of the grid-forming converter and designs a grid-forming converter system that only requires four sensors, as Figure 2As shown, the grid-forming converter system based on three voltage and one current sensor proposed by the present disclosure includes a total of three voltage sensors and one current sensor. Specifically, it includes a DC voltage sensor, a DC current sensor, and two AC capacitor voltage sensors. Among them, the two AC capacitor voltage sensors sample the two-phase capacitor voltages, and the remaining phase is obtained by Kirchhoff's voltage law. The v gfabc collected by the AC capacitor voltage sensor is the core controlled quantity. At the same time, the AC capacitor voltage sensor is also used for grid connection pre-synchronization control. The v gdc collected by the DC voltage sensor is used for duty cycle calculation, and the i gdc collected by the DC current sensor reconstructs the three-phase phase currents on the inverter side through the phase current reconstruction technology i giabc for power calculation and current limiting protection.

[0025] As an embodiment, the control process of the grid-forming converter system based on three voltage and one current sensor consists of three parts, namely the phase current reconstruction part, the inner and outer loop control part, and the feed-forward type grid connection pre-synchronization control part. Among them, the phase current reconstruction part samples the DC current i gdc and reconstructs the three-phase phase currents on the inverter side through the existing phase current reconstruction method i gi_recon . The inner and outer loop control part consists of a power control outer loop and a voltage control inner loop. The capacitor voltage v gfabc and the reconstructed current on the inverter side i gi_recon can obtain the active power p g and the reactive power q g through the power calculation module. Furthermore, by tracking the active / reactive power reference values P gref and Q gref of the active / reactive power, the phase θ g and the deviation adjustment amount ∆ v gfd of the voltage reference value are generated. The voltage inner loop closely adjusts the output capacitor voltage v gfabc of the grid-forming converter. Finally, the duty cycle of the inner loop generates a switching signal through SVPWM modulation. The system coordinate transformation and the phase of grid connection synchronization are generated by the proposed feed-forward type pre-synchronization control strategy.

[0026] The feedforward grid-connected pre-synchronization control part includes phase pre-synchronization and voltage pre-synchronization. Among them, the phase pre-synchronization control includes two stages. In the first stage, the AC relay is closed and the phase of the phase-locked capacitor voltage θ s , and in the second stage, the output phase of the phase-locked loop is maintained θ s unchanged, that is, θ s_con in the figure. The phase deviation amount is generated by the active power control, and the two are accumulated to obtain the phase of the system coordinate transformation θ g_ref .

[0027] Further, the voltage pre-synchronization control is realized by adding a voltage reference feedforward link in the voltage inner loop. Since the phase-locking and grid-connected front edge are moved from the PCC to the filter capacitor, adding voltage feedforward in the voltage inner loop can ensure that the inverter-side voltage is controlled to the grid voltage at the moment of grid connection. The output of the voltage loop control can be output after a period of time after the grid connection starts, or can be directly output, regarded as the adjustment amount of the inverter-side voltage. Because the feedforward input controls the inverter-side voltage, there is an inverter-side inductor between it and the capacitor voltage, which can thus resist the current fluctuation. Therefore, the voltage pre-synchronization control can be realized by combining the voltage reference feedforward control with the timing coordination of the inner loop output.

[0028] As an embodiment, the phase pre-synchronization process in the feedforward pre-synchronization control is as Figure 4 shown. Taking the droop control as an example for the active power control loop of the present disclosure, the phase-locked loop first locks the phase of the capacitor voltage v gfabc to obtain the phase θ s . When the grid-connected pre-synchronization is started, the output phase of the phase-locked loop is kept unchanged, that is, θ s_con . At the same time, the phase θ g is output by the active power droop control to adjust the phase θ g_ref of the system coordinate transformation and pre-synchronization, and the grid-forming converter is started.

[0029] The simulation results of the grid-connected pre-synchronization and power control of the grid-forming converter are as Figure 6 shown. Based on the grid-forming converter with three voltage and one current sensors, the grid-connected pre-synchronization process is smooth and the power control is relatively accurate. Therefore, by using the method of the present disclosure, on the basis of removing the AC current sensor and the PCC voltage sensor, the normal use of grid-connected pre-synchronization, power calculation, and current limiting protection functions can be ensured.

[0030] Embodiment 2 In one embodiment of the present disclosure, a method for a network-forming converter system based on three voltages and one current sensor is provided. The control method consists of three parts, namely, phase current reconstruction part, inner and outer loop control part, and feed-forward grid-connected pre-synchronization control part.

[0031] The phase pre-synchronization control in the feed-forward grid-connected pre-synchronization control includes two stages. In the first stage, the AC relay is closed and the phase of the locked-phase capacitor voltage is locked. In the second stage, the phase output by the phase-locked loop remains unchanged, and the phase deviation amount is generated by the active power control. The two are accumulated to obtain the phase of the system coordinate transformation. The voltage pre-synchronization control is realized by adding a voltage reference feed-forward link in the voltage inner loop. The phase-locking and grid-connected front edge are moved from the PCC to the filter capacitor. Adding voltage feed-forward in the voltage inner loop ensures that the inverter-side voltage is controlled to the grid voltage at the moment of grid connection. The output of the voltage loop control can be output after a certain period of time after the grid connection starts, or can be directly output, regarded as the adjustment amount of the inverter-side voltage.

[0032] Embodiment 3 In one embodiment of the present disclosure, a computer program product is provided, including a computer program, and when the computer program is executed by a processor, it implements the method for the network-forming converter system based on three voltages and one current sensor.

[0033] Embodiment 4 In one embodiment of the present disclosure, a non-transitory computer-readable storage medium is provided. The non-transitory computer-readable storage medium is used to store computer instructions, and when the computer instructions are executed by a processor, it implements the method for the network-forming converter system based on three voltages and one current sensor.

[0034] Embodiment 5 In one embodiment of the present disclosure, an electronic device is provided, including: a processor, a memory, and a computer program; wherein, the processor is connected to the memory, the computer program is stored in the memory, and when the electronic device runs, the processor executes the computer program stored in the memory so that the electronic device executes and implements the method for the network-forming converter system based on three voltages and one current sensor.

[0035] The present disclosure is described with reference to the flowcharts and / or block diagrams of methods, apparatuses (systems), and computer program products according to embodiments of the present disclosure. It should be understood that each flow and / or block in the flowcharts and / or block diagrams, and the combination of flows and / or blocks in the flowcharts and / or block diagrams, can be implemented by computer program instructions. These computer program instructions can be provided to the processor of a general-purpose computer, a special-purpose computer, an embedded processor, or other programmable data processing devices to generate a machine, so that the instructions executed by the processor of the computer or other programmable data processing devices generate for implementing in the processFigure 1 one process or multiple processes and / or blocks Figure 1 a device for the functions specified in one block or multiple blocks.

[0036] These computer program instructions can also be loaded onto a computer or other programmable data processing device, so that a series of operation steps are executed on the computer or other programmable device to generate a computer-implemented process. Thus, the instructions executed on the computer or other programmable device provide for implementing the steps of the functions specified in one process Figure 1 one process or multiple processes and / or blocks Figure 1 in one block or multiple blocks.

[0037] Although the specific embodiments of the present disclosure have been described above in conjunction with the accompanying drawings, this is not a limitation on the protection scope of the present disclosure. Those skilled in the art should understand that, based on the technical solutions of the present disclosure, various modifications or deformations that can be made by those skilled in the art without creative efforts are still within the protection scope of the present disclosure.

Claims

1. A grid-forming converter system based on three voltage and one current sensors, characterized in that, The grid-forming converter system includes a total of three voltage sensors and one current sensor; Among them, the voltage sensors include one DC voltage sensor and two AC capacitor voltage sensors, and the current sensor is one DC current sensor. The DC voltage sensor is used to calculate the duty cycle in the voltage inner loop. The DC current sensor is used to reconstruct the three-phase phase currents on the inverter side. The three-phase phase currents on the inverter side are used for power calculation and current limiting protection. The AC capacitor voltage sensors are used for inner-loop capacitor voltage control, sampling the two-phase capacitor voltages and calculating the remaining phase capacitor voltage, and using the AC capacitor voltage sensors for grid connection pre-synchronization control.

2. The grid-forming converter system based on three voltage and one current sensors according to claim 1, characterized in that, The grid-forming converter system with three voltage and one current sensors specifically includes one DC voltage sensor, one DC current sensor, and two AC capacitor voltage sensors. The two AC capacitor voltage sensors sample the two-phase capacitor voltages, and the remaining phase is calculated by Kirchhoff's voltage law. The voltage collected by the AC capacitor voltage sensors is the core controlled quantity. At the same time, the AC capacitor voltage sensors are also used in the grid connection pre-synchronization control. The voltage pre-synchronization control is realized by the time sequence coordination of the voltage reference value feed-forward control combined with the output quantity of the inner loop. The phase pre-synchronization control is realized by the stage coordination of the phase of the capacitor voltage locked by the phase-locked loop and the output phase of the active power control.

3. The network-forming converter system based on three voltage and one current sensors as claimed in claim 1, wherein In the feed-forward type grid connection pre-synchronization control, the voltage pre-synchronization control is realized by adding a voltage reference value feed-forward link in the voltage inner loop. The phase-locking and grid connection front edge are moved from the PCC to the filter capacitor. Adding voltage feed-forward in the voltage inner loop ensures that the inverter side voltage is controlled to the grid voltage at the moment of grid connection. The output quantity of the voltage loop control is directly output after the grid connection is started, and the output quantity of the voltage loop control is regarded as the adjustment quantity of the inverter side voltage.

4. The network-forming converter system based on three voltage and one current sensors according to claim 1, characterized in that, The phase pre-synchronization control in the feed-forward type grid connection pre-synchronization control includes two stages. In stage 1, the AC relay is closed, and the phase of the capacitor voltage locked by the phase-locked loop is obtained. In stage 2, that is, when the grid connection pre-synchronization is started, the output phase of the phase-locked loop remains unchanged. At the same time, the output phase of the active power control adjusts the phase of the system coordinate transformation and pre-synchronization, and the grid-forming converter is started.

5. The method of the grid-forming converter system based on three voltage and one current sensors according to any one of claims 1-4, characterized in that, The control method consists of three parts, namely the phase current reconstruction part, the inner and outer loop control part, and the feed-forward type grid connection pre-synchronization control part.

6. The method of the grid-forming converter system based on three voltage and one current sensors according to claim 5, characterized in that, The phase pre-synchronization control in the feed-forward type grid connection pre-synchronization control includes two stages. In the first stage, the AC relay is closed and the phase of the locked capacitor voltage is obtained. In the second stage, the output phase of the phase-locked loop remains unchanged. The phase deviation quantity is generated by the active power control, and the two are accumulated to obtain the phase of the system coordinate transformation. The voltage pre-synchronization control is realized by adding a voltage reference value feed-forward link in the voltage inner loop. The phase-locking and grid connection front edge are moved from the PCC to the filter capacitor. Adding voltage feed-forward in the voltage inner loop ensures that the inverter side voltage is controlled to the grid voltage at the moment of grid connection. The output quantity of the voltage loop control is directly output after the grid connection is started, and is regarded as the adjustment quantity of the inverter side voltage.

7. The method of the grid-forming converter system based on three voltage and one current sensors according to claim 5, characterized in that, The phase pre-synchronization control in the feed-forward grid-connected pre-synchronization control includes two stages. In stage 1, the AC relay is closed, and the phase of the voltage across the phase-locked loop capacitor is obtained. In stage 2, that is, when the grid-connected pre-synchronization is started, the output phase of the phase-locked loop is kept unchanged. At the same time, the output phase of the active power control is used to adjust the phase of the system coordinate transformation and pre-synchronization, and the grid-forming converter is started.

8. A computer program product, comprising a computer program, characterized in that, When the computer program is executed by a processor, it implements the method of the grid-forming converter system based on three voltage and one current sensors according to any one of claims 5-7.

9. A non-transitory computer-readable storage medium, characterized in that, The non-transitory computer-readable storage medium is used to store computer instructions. When the computer instructions are executed by a processor, the method of the grid-forming converter system based on three voltage and one current sensors according to any one of claims 5-7 is implemented.

10. An electronic device, characterized in that, Including: A processor, a memory, and a computer program; wherein, the processor is connected to the memory, the computer program is stored in the memory, and when the electronic device runs, the processor executes the computer program stored in the memory so that the electronic device executes the method of the grid-forming converter system based on three voltage and one current sensors according to any one of claims 5-7.

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